You've got a great base to start with there! My best advice would be to render out a heightmap or mesh at as high of a resolution as your system can handle, then pull the model or heightmap into a program that will let you sculpt the actual terrain. I've never seen World Machine do vertical crevices like that on a sheer face, though it is probably possible with enough work. Especially if you want that cave at the bottom, though, that's going to be actually impossible in World Machine. Proper sculpting will help you get those sharp faces, as well as the finer detail in the cracks and rock layering.

I'm by no means an expert, so ymmv, but I find World Machine to be an amazing tool to make the base terrain, but a fully fledged sculpting program such as ZBrush to make more detailed features.